title: Prevention of motion-induced signal loss in diffusion-weighted echo-planar imaging by dynamic restoration of gradient moments.
abstract: OBJECTIVE
  Head motion is a significant problem in diffusion-weighted imaging as it may cause signal attenuation due to residual dephasing during strong diffusion encoding gradients even in single-shot acquisitions. Here, we present a new real-time method to prevent motion-induced signal loss in DWI of the brain.
  
  
  METHODS
  The method requires a fast motion tracking system (optical in the current implementation). Two alterations were made to a standard diffusion-weighted echo-planar imaging sequence: first, real-time motion correction ensures that slices are correctly aligned relative to the moving brain. Second, the tracking data are used to calculate the motion-induced gradient moment imbalance which occurs during the diffusion encoding periods, and a brief gradient blip is inserted immediately prior to the signal readout to restore the gradient moment balance.
  
  
  RESULTS
  Phantom experiments show that the direction as well as magnitude of the gradient moment imbalance affects the characteristics of unwanted signal attenuation. In human subjects, the addition of a moment-restoring blip prevented signal loss and improved the reproducibility and reliability of diffusion tensor measures even in the presence of substantial head movements.
  
  
  CONCLUSIONS
  The method presented can improve robustness for clinical routine scanning in populations that are prone to head movements, such as children and uncooperative adult patients.
authors.affiliation: Department of Medicine, JABSOM, University of Hawaii, Honolulu, Hawaii, USA.
authors.forename: Kazim
authors.initials: K
authors.lastname: Gumus
authors.forename: Brian
authors.initials: B
authors.lastname: Keating
authors.forename: Benedikt A
authors.initials: BA
authors.lastname: Poser
authors.forename: Brian
authors.initials: B
authors.lastname: Armstrong
authors.forename: Linda
authors.initials: L
authors.lastname: Chang
authors.forename: Julian
authors.initials: J
authors.lastname: Maclaren
authors.forename: Thomas
authors.initials: T
authors.lastname: Prieto
authors.forename: Oliver
authors.initials: O
authors.lastname: Speck
authors.forename: Maxim
authors.initials: M
authors.lastname: Zaitsev
authors.forename: Thomas
authors.initials: T
authors.lastname: Ernst
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D017352:Echo-Planar Imaging / Q000379:methods; D019416:Head Movements; D064368:Healthy Volunteers; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D009038:Motion; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted
keywords: diffusion weighted imaging; gradient moment restoration; real-time motion tracking; signal loss